Some basic knowledge
Link State Protocol
- Routing protocol used in packet switching ex includes: OSPF, IS-IS.
- Basic idea:
- Every node constructs a map of connectivity to the network in terms of a graph, which shows that which nodes are connected to other.
- Each node then computes best logical path (using Dijkstra) from it to the destination.
- These best path then form the node’s routing table
Intermediate System to Intermediate System (IS-IS)
- This routing protocol was designed for routing packets at Layer 2 very similar to OSFP at Layer 3.
- Both of them uses Dijkstra to compute the shortest path and can use multicast to discover neighboring routers.
- IS-IS routers build a topological representation of the network. This map indicates the subnets which each IS-IS router can reach, and the lowest-cost (shortest) path to a subnet is used to forward traffic.
TRILL
It is implemented by devices called RBridges which a link-state protocol among themselves. Some benefits of TRILL:
- It runs directly over Layer 2 as it uses IS-IS so no configuration is required like IP Address
- It is easy to extend the protocol by adding an extra field value in the header for carrying TRILL information
Mitigation of Loops
- Forward packets on a header with hop count.
- RBridges also specify the next hop RBridge as the frame destination when forwarding unicast frames across a shared-media link, which avoids spawning additional copies of frames during a temporary loop
- Also perform reverse path forwarding check on multi destination frames to avoid loops
